The application of lithium currently extends to diverse industries, including the rechargeable battery, glass, ceramic, alloy, lubricant, and pharmaceutical industries. The lithium rechargeable battery has recently been receiving attention as a main power source for hybrid and electric cars, and the market for lithium rechargeable batteries for cars is expected to continue growing to approximately one-hundred times the conventional compact battery markets for cell phones and notebooks.
In addition, a global movement towards more stringent environmental regulations is likely to expand the application of lithium to not only the hybrid and electric car industries, but to the electrical, chemical and energy fields as well. Thus, a dramatic increase of both domestic and foreign demand for lithium is expected.
Some notable main sources for the lithium could be brine containing lithium produced in nature, and a lithium bearing solution supplied from minerals possessing lithium. Such lithium bearing solution, however, contains a substantial amount of impurities, including magnesium, boron and calcium. The extraction of the impurities in advance is considered to be a critical process in order to obtain high purity lithium necessary for preparing a lithium rechargeable battery.
Conventionally, after absorbed on a boron-selective ion exchange resin containing a N-methylglucamine functional group, the boron ions included in a lithium bearing solution are extracted by washing with an acid solution for desorption. The magnesium and calcium ions included in the lithium bearing solution are extracted by adding alkali and precipitating in the form of magnesium hydroxide and calcium hydroxide.
Such method, however, is not suitable for extracting the boron from the lithium bearing solution, because a relatively expensive ion-exchange resin and usage of a variety of chemicals (e.g., substantial amounts of an acid and a base) in the management of the boron-extracting process are required. Further, the loss of lithium is likely to be substantial because the addition of excessive alkali elevates the pH of the lithium bearing solution, which, in turn, causes a negative charge to be built up on the surface of the precipitated magnesium hydroxide and calcium hydroxide, and thus the absorption of positive lithium ions. As a result, the extraction of lithium along with the impurities cannot be avoided.
U.S. Pat. No. 5,219,550 describes a method of eliminating impurities by extracting magnesium and calcium from the brine after the extraction of boron in an organic phase by mixing an organic solvent with lithium bearing brine at a volume ratio from 1:1 to 5:1. This complicated process, however, has some drawbacks, namely environmental pollution caused by using the organic solvent and a substantial loss of lithium due to the uncontrolled pH.